Resin containing phosphate group

ABSTRACT

The present invention relates to a phosphate group-containing resin obtained by copolymerizing:  
     (a) a polymerizable monomer having a phosphate group represented by a formula [—OPO(OR)(OH)] (wherein R represents a hydrocarbon group having 4 to 10 carbon atoms), (b) a polymerizable monomer having a phosphoric acid group represented by a formula [—OPO(OH) 2 ] and (c) a (meth)acrylate base polymerizable monomer having two tertiary alkyl groups in a molecule and to a water based metallic coating material composition comprising the above phosphate group-containing resin and a metallic pigment.

TECHNICAL FIELD

[0001] The present invention relates to a novel phosphategroup-containing resin and a water based metallic coating materialcomposition comprising the above phosphate group-containing resin.

BACKGROUND ART

[0002] A water based metallic coating material containing a metallicpigment such as aluminum flake has the problem that the metallic pigmentis brought into contact with a large amount of water contained in thecoating material and corroded to generate hydrogen gas. In order tosolve this problem, it is proposed that phosphoric acid esters are addedto a water based metallic coating material to protect the surface of ametallic pigment with the phosphoric acid esters making use of anadsorptive action exerted by an acidic hydroxyl group bonded to aphosphorus atom of the above esters to inhibit reaction caused by directcontact of water with the metallic pigment. However, it is difficult toinhibit this reaction over a long period of time in a water basedmetallic coating material comprising such phosphoric acid esters, and ametallic coating film formed has the defect that an adhesive property, awater resistance, a chipping resistance and a metallic; finish feelingare not satisfactory.

[0003] Disclosed respectively are a water based metallic coatingmaterial comprising an aluminum flake treated with a phosphoric acidester in Japanese Patent Application Laid-Open No.168670/1983, a waterbased metallic coating material comprising a phosphoric acid ester ofcaprolactone in Japanese Patent Application Laid-Open No.29607/1986, awater based metallic coating material comprising a reaction product oforthophosphoric acid and an epoxy compound in Japanese PatentApplication Laid-Open No.47771/1986, a water based metallic coatingmaterial comprising a phosphate-containing acryl polymer obtained fromorthophosphoric acid and a glycidy group-containing acryl polymer inJapanese Patent Application Laid-Open No. 190765/1989 and a water basedmetallic coating material comprising a polymer of styrene and allylalcohol and a reaction product of p-t-amylphenol and orthophosphoricacid or phosphorus pentaoxide in Japanese Patent PublicationNo.46624/1990. However, all of these water based metallic coatingmaterials have the defect that the coating films thereof are notsatisfactory in an adhesive property, a water resistance and a metallicappearance.

DISCLOSURE OF THE INVENTION

[0004] It has been found that a phosphate group-containing resin whichis a copolymer of two kinds of some specific phosphate group-containingpolymerizable monomers and a polymerizable monomer having two tertiaryalkyl groups in a molecule is excellent in an adsorptive property to thesurface of a metallic pigment and effective for inhibiting a reaction ofwater with a metallic pigment over a long period of time and that acoating film formed from a water based metallic coating materialcomprising such phosphate group-containing resin is excellent inperformances such as an adhesive property, a water resistance, achipping resistance and a metallic finish feeling.

[0005] Thus, according to the present invention, provided is a phosphategroup-containing resin obtained by copolymerizing:

[0006] (a) a polymerizable monomer having a phosphate group representedby a formula [—OPO(OR)(OH)] (wherein R represents a hydrocarbon grouphaving 4 to 10 carbon atoms),

[0007] (b) a polymerizable monomer having a phosphoric acid grouprepresented by a formula [—OPO(OH)₂] and

[0008] (c) a (meth)acrylate base polymerizable monomer having twotertiary alkyl groups in a molecule, which is represented by:

[0009] wherein X represents hydrogen or methyl.

[0010] Further, according to the present invention, provided is a waterbased metallic coating material composition comprising the phosphategroup-containing resin described above and a metallic pigment.

[0011] The phosphate group-containing resin and the water based metalliccoating material composition which are provided by the present inventionshall be explained below in further details.

EMBODIMENT OF THE INVENTION

[0012] Polymerizable monomer (a) having a phosphoric acid monoestergroup:

[0013] The polymerizable monomer (a) is a phosphoric acid diestercompound having each at least one phosphate group represented by aformula [—OPO(OR)(OH)] and polymerizable double bond in a molecule,wherein R represents a hydrocarbon group having 4 to 10 carbon atoms,and to be specific, it includes, for example, linear or branched chainalkyl groups such as butyl, isobutyl, sec-butyl, tert-butyl, pentyl,isopentyl, hexyl, octyl, 2-ethylhexyl, decyl and isodecyl.

[0014] Included in the polymerizable monomer (a) are those obtained byreacting, for example, one acidic hydroxyl group contained in aphosphoric acid monoester represented by (HO)₂PO(OR), for example,phosphate such as monobutyl phosphate (R═C₄H₉) and monoisodecylphosphate (R═C₁₀H₂₁) with a glycidyl group-containing compound having apolymerizable double bond, for example, glycidyl acrylate and glycidylmethacrylate.

[0015] Polymerizable monomer (b) having a phosphoric acid group:

[0016] The polymerizable monomer (b) is a compound having each at leastone a phosphoric acid group represented by a formula [—OPO(OH)₂] andpolymerizable double bond in a molecule, and to be specific, itincludes, for example, (2-acryloyloxyethyl) acid phosphate,(2-methacryloyloxyethyl) acid phosphate, (2-acryloyloxypropyl) acidphosphate and (2-methacryloyloxypropyl) acid phosphate.

[0017] (Meth)acrylate base polymerizable monomer (c):

[0018] The polymerizable monomer (c) is a compound represented by:

[0019] (wherein X represents hydrogen or methyl) in a molecule, and ithas two tertiary alkyl groups in a molecule, in which three methylgroups are bonded to one carbon atom. Use of this monomer (c) makes iteasy to allow metallic flakes to be aligned parallel to the coated facein the water based metallic coating material of the present inventionand makes it possible to elevate the metallic appearance of the coatingfilm.

[0020] Other polymerizable monomer (d):

[0021] The phosphate group-containing resin of the present invention isobtained by copolymerizing as essential components, the polymerizablemonomer (a), the polymerizable monomer (b) and the polymerizable monomer(c) each described above, and if necessary, the other polymerizablemonomer (d) in addition thereto can be used in combination as acopolymerization component.

[0022] The other polymerizable monomer (d) is a compound having at leastone polymerizable double bond in a molecule other than the polymerizablemonomers (a), (b) and (c) each described above, and it includescompounds exemplified below.

[0023] 1) (Meth)acrylate base monomers: for example, C₁ to C₂₄ alkylesters of (meth)acrylic acid such as methyl methacrylate, ethyl(meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate,2-ethylhexyl (meth)acrylate and lauryl (meth)acrylate.

[0024] 2) Hydroxyl group-containing monomers: for example, C₂ to C₁₀hydroxyalkyl esters of (meth)acrylic acid, such as hydroxyethyl(meth)acrylate and hydroxypropyl (meth)acrylate.

[0025] 3) Carboxyl group-containing monomers: for example, unsaturatedcarboxylic acids and anhydrides thereof such as (meth)acrylic acid,maleic acid and maleic anhydride.

[0026] 4) Other monomers: for example, vinyl aromatic compounds such asstyrene, α-methylstyrene and vinyltoluene, (meth)acrylonitrile and vinylacetate.

[0027] The phosphate group-containing resin of the present invention canbe produced by copolymerizing the polymerizable monomers (a) to (d) eachdescribed above in the presence of a polymerization initiator by aconventionally known method, for example, a solution polymerizationmethod. A use proportion of these polymerizable monomers incopolymerization shall not strictly be restricted and can be changedover a wide range depending on characteristics desired to the phosphategroup-containing resin produced. In general, it can fall in thefollowing range based on the total amount of the polymerizable monomers(a) to (d):

[0028] polymerizable monomer (a): 0.5 to 30% by weight, preferably 1 to20% by weight and particularly preferably 1.5 to 15% by weight,

[0029] polymerizable monomer (b): 1 to 35% by weight, preferably 3 to20% by weight and particularly preferably 5 to 18% by weight,

[0030] polymerizable monomer (c): 3 to 35% by weight, preferably 5 to30% by weight and particularly preferably 8 to 25% by weight, and

[0031] polymerizable monomer (d): 0 to 95.5% by weight, preferably 30 to91% by weight and particularly preferably 42 to 85.5% by weight.

[0032] The phosphate group-containing resin of the present invention canhave a weight average molecular weight falling in a range of usually3,000 to 100,000, preferably 5,000 to 50,000 and particularly preferably5,000 to 30,000 and an acid value falling in a range of 20 to 140mgKOH/g, particularly 40 to 120 mgKOH/g and further particularly 50 to100 mgKOH/g originating in a phosphoric acid group. Further, thephosphate group-containing resin of the present invention can contain,if necessary, a carboxyl group and/or a hydroxyl group, and a content ofthese groups falls preferably in a range of 100 mgKOH/g or less,particularly 0 to 80 mgKOH/g in terms of an acid value originating in acarboxyl group and 0 to 120 mgKOH/g, particularly 15 to 100 mgKOH/g interms of a hydroxyl value.

[0033] Water based metallic coating material composition:

[0034] The phosphate group-containing resin provided by the presentinvention is very useful as a passivator for the metallic pigment in thewater based metallic coating material and not only protects the metallicpigment from corrosion caused by reaction with water over a long periodof time but also is excellent in an aligning property of the metallicpigment, and blending of the phosphate group-containing resin makes itpossible to provide the water based metallic coating materialcomposition which is excellent in a storage stability and excellent aswell in coating film performances such as an adhesive property, a waterresistance, a chipping resistance and a metallic finish feeling.

[0035] Thus, according to the present invention, provided is the waterbased metallic coating material composition comprising the phosphategroup-containing resin of the present invention and the metallicpigment.

[0036] The water based metallic coating material composition of thepresent invention can be prepared by mixing and dispersing a base resin,a curing agent, the phosphate group-containing resin of the presentinvention and the metallic pigment and, if necessary, the other coatingmaterial additives in a water based medium.

[0037] Conventionally known resins which have so far been used for waterbased coating materials can be used as the base resin and includes, forexample, water-soluble or water-dispersible reins such as alkyd resins,acryl resins, polyester resins and urethane resins. These resins havepreferably cross-linking functional groups such as a hydroxyl group, acarboxyl group and an epoxy group in the molecules thereof. The curingagent includes melamine resins, blocked polyisocyanate compounds, epoxycompounds and carboxyl group-containing compounds which can be reactedwith these functional groups. A blending proportion of the base resinand the curing agent falls suitably in a range of 50 to 90%,particularly 60 to 80% in the former case and 50 to 10%, particularly 40to 20% in the latter case each based on the total solid matter weight ofthe both.

[0038] The metallic pigment is a pigment which provides the coating filmwith a sparkling brilliant feeling and a light coherent pattern, and tobe specific, capable of being used is at least one pigment selected fromnon-leafing type or leafing type aluminum (including depositedaluminum), aluminum oxide, copper, zinc, brass, nickel, mica and micascoated with titanium oxide and iron oxide. These metallic pigments arepreferably flake-shaped. A blending proportion of the metallic pigmentfalls suitably in a range of usually 1 to 50 parts by weight,particularly 5 to 30 parts by weight per 100 parts by weight of thetotal of the base resin and the curing agent.

[0039] A blending proportion of the phosphate group-containing resin ofthe present invention falls suitably in a range of usually 0.1 to 15parts by weight, particularly 0.5 to 10 parts by weight in terms of asolid matter per 100 parts by weight of the metallic pigment.

[0040] The phosphate group-containing resin of the present invention canbe neutralized in advance with a base such as, for example, ammonia,dimethylamine, triethylamine, ethanolamine and dimethylethanolamineprior to blending with the coating material.

[0041] The water based metallic coating material composition of thepresent invention can be prepared, for example, by mixing and dispersingthe base resin, the curing agent, the phosphate group-containing resinof the present invention and the metallic pigment each described above,if necessary, together with coating material additives such as a solidcolor pigment, an extender pigment, a hydrophilic organic solvent, asurface controlling agent and a settling inhibitor in a water basedmedium by a conventionally known method. In this case, the phosphategroup-containing resin of the present invention and the metallic pigmentare preferably mixed in advance, and the mixture thereof is preferablymixed and dispersed in a water based medium together with the base resinand the curing agent. To be more specific, the metallic pigment ishomogeneously mixed with the phosphate group-containing resin solutionof the present invention in which a solid matter content is controlledto 40 to 70% by weight in the proportion described above to adsorb thephosphate group-containing resin on the surface of the metallic pigment,and it is then neutralized with the base described above and dispersed.Then, it is preferably mixed and dispersed in water together with thebase resin and the curing agent.

[0042] The coating material composition of the present invention can becoated directly on an article to be coated such as a metal-made orplastic-made automobile outside plate. In general, an undercoatingmaterial such as an electrodepositable coating material and, ifnecessary, an intermediate coating material are coated thereon inadvance, and these coating films are cured. Then, the coating materialcomposition of the present invention is preferably coated on the coatedface thereof. A viscosity of the coating material composition of thepresent invention is controlled to a range of 10 to 30 seconds/Ford cup#4/20° C. and preferably coated d by a method such as airless spray, airspray and an electrostatic method so that a film thickness is 10 to 40μm in terms of a cured film thickness. The metallic coating film thusformed can usually be cured by heating at a temperature of about 100 toabout 170° C. for 10 to 40 minutes. Further, after curing this metalliccoating film or without curing it, a clear coating material can furtherbe coated on this metallic coated face.

EXAMPLES

[0043] The present invention shall more specifically be explained belowwith reference to examples related to the present invention andcomparative examples. Both of parts and percentage are based on weight,and a thickness of the coating film is that of the cured coating film.

Example 1

[0044] A reactor equipped with a stirrer, a temperature-controller and acondenser was charged with a mixed solvent of 27.5 parts ofmethoxypropanol and 27.5 parts of isobutanol and heated to 110° C. Itwas maintained at the same temperature, and then dropwise added to themixed solvent described above in 4 hours was 121.5 parts of a mixturecomprising 25 parts of styrene, 27.5 parts of n-butyl methacrylate, 20parts of “Isostearyl Acrylate” (trade name, corresponding to thepolymerizable monomer (c), manufactured by Osaka Organic Chemical Co.,Ltd.), 7.5 parts of 4-hydroxybutyl acrylate, 15 parts of a phosphategroup-containing polymerizable monomer (a1) (remark 1), 12.5 parts of2-methacryloyloxyethyl acid phosphate (corresponding to thepolymerizable monomer (b)), 10 parts of isobutanol and 4 parts oft-butylperoxyoctanoate. Further, a mixture comprising 0.5 part oft-butylperoxyoctanoate and 20 parts of isopropanol was dropwise addedthereto in one hour. Then, the mixture was stirred and ripened for onehour to obtain a phosphate group-containing resin solution (I). Theabove resin had an acid value of 83 mgKOH/g originating in a phosphategroup, a hydroxyl group value of 29.2 mgKOH/g originating in4-hydroxybutyl acrylate, a weight average molecular weight of 10000 anda solid matter content of 50%.

[0045] (Remark 1) Phosphate group-containing polymerizable monomer (a1):A reactor equipped with a stirrer, a temperature-controller and acondenser was charged with 57.55 parts of monobutyl phosphate and 41.1parts of isobutanol, and 42.45 parts of glycidyl methacrylate wasdropwise added thereto in 2 hours under air flow, followed by furtherstirring and ripening for one hour. Then, 58.88 parts of isopropanol wasadded to dilute the solution to obtain a phosphate group-containingpolymerizable monomer. It had an acid value of 285 mgKOH/g originatingin a phosphoric acid group and a solid matter content of 50%.

Example 2

[0046] A reactor equipped with a stirrer, a temperature-controller and acondenser was charged with a mixed solvent of 27.5 parts ofmethoxypropanol and 27.5 parts of isobutanol and heated to 110° C. Itwas maintained at the same temperature, and then dropwise added to themixed solvent described above in 4 hours was 121.5 parts of a mixturecomprising 50 parts of styrene, 7.5 parts of n-butyl methacrylate, 15parts of “Isostearyl Acrylate” (trade name, corresponding to thepolymerizable monomer (c), manufactured by Osaka Organic Chemical Co.,Ltd.), 7.5 parts of 4-hydroxybutyl acrylate, 15 parts of the phosphategroup-containing polymerizable monomer (a1) (remark 1), 12.5 parts of2-methacryloyloxyethyl acid phosphate (corresponding to thepolymerizable monomer (b)), 10 parts of isobutanol and 4 parts oft-butylperoxyoctanoate. Further, a mixture comprising 0.5 part oft-butylperoxyoctanoate and 20 parts of isopropanol was dropwise addedthereto in one hour. Then, the mixture was stirred and ripened for onehour to obtain a phosphate group-containing resin solution (II). Theabove resin had an acid value of 83 mgKOH/g originating in a phosphoricacid group, a hydroxyl group value of 29.2 mgKOH/g originating in4-hydroxybutyl acrylate, a weight average molecular weight of 10000 anda solid matter content of 50%.

Example 3

[0047] Mixed were 18.06 parts of “Alpaste 891K” (trade name,manufactured by Toyo Aluminum Co., Ltd., flaky aluminum metallic pigmentpaste, aluminum pigment content: 72%), 12.5 parts of butyl cellosolve,6.25 parts of hexyl cellosolve and 6.25 parts of “Shellsol 71L” (tradename, manufactured by Showa Shell Co., Ltd., hydrocarbon base organicsolvent), and the mixture was stirred until the aluminum pigment washomogeneously dispersed. Then, 3.92 parts of the resin solution (I)obtained in Example 1 and 0.2 part of methylethanolamine were added tothis mixture to neutralize it, and the mixture was stirred for one hour.Next, 40 parts of an acryl emulsion (remark 2) was added to this mixturewhile stirring, and 62.72 parts of deionized water was then added todilute the mixture, followed by stirring for one hour to obtain a millbase.

[0048] Added to 160 parts of the acryl emulsion (remark 2) were 33.33parts of “90% Cymel 327” (trade name, manufactured by Mitsui Cytec Co.,Ltd., melamine resin) and 57.14 parts of a 35% polyester aqueoussolution (remark 3), and the mixture was stirred for 15 minutes. Then,150 parts of the mill base described above was added thereto and stirredfor 30 minutes, and deionized water and methylethanolamine were thenadded to obtain a water based metallic coating material having a pH of8.4 to 8.5 and a solid matter content of 25%.

[0049] (Remark 2) Acryl emulsion: A reactor equipped with a stirrer, atemperature-controller and a condenser was charged with 32.1 parts ofdeionized water and 0.267 part of “N-562SF” (emulsifier, manufactured byNippon Nyukazai Co., Ltd.) and heated to 80° C., and then 0.033 part ofammonium persulfate dissolved in 1.110 part of deionized water was addedthereto to ripen the mixture for 20 minutes. Then, mixed were 14.45parts of methyl methacrylate, 7.12 parts of n-butyl methacrylate, 0.67part of allyl methacrylate, 21.63 parts of deionized water and 0.267part of “N-562SF” to prepare a pre-emulsion, and the resultingpre-emulsion was dropwise added to the reactor in 2 hours, followed byripening it for one hour. Then, mixed were 2.29 parts of methylmethacrylate, 2.48 parts of n-butyl methacrylate, 0.98 part of2-hydroxyethyl acrylate, 0.78 part of methacrylic acid, 9.77 parts ofdeionized water and 0.114 part of “N-562SF” to prepare a pre-emulsion,and the resulting pre-emulsion was dropwise added to the reactor in 2hours. A solution prepared by dissolving 0.003 part of ammoniumpersulfate in 1.110 part of deionized water was dropwise added togetherwith this emulsion in 2 hours. Then, the emulsion was ripened for onehour, and A solution prepared by dissolving 0.294 part ofdimethylethanolamine in 19.53 parts of deionized water was addedthereto. The emulsion thus obtained had a solid matter content of 25%, apH of 8.5 and a particle diameter of 120 nm.

[0050] (Remark 3) 35% Polyester aqueous solution: A reactor equippedwith a stirrer, a partial condenser, a whole condenser and a torquemeter was charged with 78.75 parts (0.75 mole) of neopentyl glycol,34.13 parts (0.25 mole) of trimethylolpropane, 65.7 parts (0.45 mole) ofadipic acid and 74.7 parts (0.45 mole) of isophthalic acid and heatedfrom 150 to 230° C. in 3 hours, and it was maintained at the sametemperature for 1.5 hour to carry out condensation reaction whileallowing condensed water to flow out to the outside of the system. Then,3 parts of toluene was added thereto to continue stirring anddehydration while refluxing to carry out reaction until an acid valueoriginating in a carboxyl group became 8 mgKOH/g, and resulting waterwas removed by subjecting it to azeotropy with toluene. Then, thetemperature was lowered to 170° C., and 6.72 parts (0.035 mole) oftrimellitic anhydride was added thereto. The solution was ripened at thesame temperature for 30 minutes, and then 20 parts of butylcarbitol wasadded thereto, followed by reducing the temperature to 80° C.

[0051] A water-soluble polyester resin thus obtained had an acid valueof 25 mgKOH/g, a hydroxyl group value of 93 mgKOH/g and a number averagemolecular weight of 1700. Added thereto was 9 parts ofdimethylethanolamine to neutralize the solution, and the solid mattercontent was adjusted to 35% by deionized water.

Example 4

[0052] Mixed were 18.06 parts of “Alpaste 891K”, 12.5 parts of butylcellosolve, 6.25 parts of hexyl cellosolve and 6.25 parts of “Shellsol71L”, and the mixture was stirred until the aluminum pigment washomogeneously dispersed. Then, 3.92 parts of the resin solution (II)obtained in Example 2 and 0.2 part of methylethanolamine were added tothis mixture to neutralize it, and the mixture was stirred for one hour.Next, 40 parts of the acryl emulsion (remark 2) was added to thismixture while stirring, and 62.72 parts of deionized water was thenadded to dilute the mixture, followed by stirring for one hour to obtaina mill base.

[0053] Added to 160 parts of the acryl emulsion (remark 2) were 33.33parts of “90% Cymel 327” and 57.14 parts of the 35% polyester aqueoussolution (remark 3), and the mixture was stirred for 15 minutes. Then,150 parts of the mill base described above was added thereto and stirredfor 30 minutes, and deionized water and methylethanolamine were thenadded to obtain a water based metallic coating material having a pH of8.4 to 8.5 and a solid matter content of 25%.

Comparative Example 1

[0054] Mixed were 18.06 parts of “Alpaste 891K”, 12.5 parts of butylcellosolve, 6.25 parts of hexyl cellosolve and 6.25 parts of “Shellsol71L”, and the mixture was stirred until the aluminum pigment washomogeneously dispersed. Next, 40 parts of the acryl emulsion (remark 2)was added to this mixture while stirring, and 62.72 parts of deionizedwater was then added to dilute the mixture, followed by stirring for onehour to obtain a mill base.

[0055] Added to 160 parts of the acryl emulsion (remark 2) were 33.33parts of “90% Cymel 327” and 57.14 parts of the 35% polyester aqueoussolution (remark 3), and the mixture was stirred for 15 minutes. Then,150 parts of the mill base described above was added thereto and stirredfor 30 minutes, and deionized water and methylethanolamine were thenadded to obtain a water based metallic coating material having a pH of8.4 to 8.5 and a solid matter content of 25%.

Comparative Example 2

[0056] According to descriptions of Japanese Patent ApplicationLaid-Open No.190765/1989, a reactor of one liter equipped with astirrer, a thermometer and a condenser was charged with 183 parts ofethylene glycol monobutyl ether and heated to 130° C., and dropwiseadded thereto at the same temperature in 3 hours were a monomer solutioncomprising 69.6 parts of glycidyl methacrylate, 144.01 parts ofhydroxyethyl methacrylate, 98.4 parts of methyl methacrylate and 120parts of lauryl methacrylate and 96 parts of a xylene solutioncontaining 24 parts of azobisisobutyronitrile to react them. After 30minutes passed since finishing dropwise adding, 32 parts of a xylenesolution containing 3 parts of azobisisobutyronitrile was furtherdropwise added in 15 minutes. Then, stirring was continued at 130° C.for 2 hours to react them. The resulting mixed solution was cooled downto 50° C., and 56.5 parts of phosphoric acid (85% aqueous solution) wasadded thereto, and the solution was maintained at 50° C. for 2 hours tofinish the reaction. It had a solid matter content of 54.5%, an acidvalue of 71 mgKOH/g and a number averaged molecular weight of 3000.

[0057] Then, a water based metallic coating material was obtained in thesame manner as in Example 3, except that 3.6 parts of the reactionproduct (solid matter content: 54.5%) described above was substitutedfor 3.92 parts of the resin solution (I) obtained in Example 3. It had apH of 8.4 to 8.5 and a solid matter content of 25%.

Comparative Example 3

[0058] According to descriptions of Japanese Patent Publication No.46624/1990, a mixture of a styrene/allyl alcohol (1.57:1 weight ratio)copolymer having a molecular weight of 1150 (104.7 parts, 1.0 mole),p-tert-amylphenol (44.5 parts, 3 mole) and xylene (168.6 parts) washeated and stirred at 85 to 90° C. in a reactor equipped with a stirrer,a thermometer, a reflux condenser and a Dean and Stark separator untilthe solid component was dissolved. Then, phosphorus pentaoxide (19.4parts, 1.5 mole) and an additional part (20 parts) of xylene were addedthereto, and the temperature was elevated to a reflux temperature (140to 143° C.) of the diluent (xylene). After 3 hours, 1.2 part of waterwas removed. Then, the reaction mixture was distilled under vacuum for30 minutes to remove xylene (132 parts). This xylene was substitutedwith isobutanol (90.8 parts) added in 10 minutes. A corrosion inhibitorsolution thus obtained had a solid matter content of 53.6% and an acidvalue of 114 mgKOH/g.

[0059] Then, a water based metallic coating material was prepared in thesame manner as in Example 1, except that 3.65 parts of the corrosioninhibitor solution described above was added in place of the phosphategroup-containing resin obtained in Example 1 and that the solution wasneutralized with 0.28 part of methylethanolamine.

Comparative Example 4

[0060] Mixed were 18.06 parts of “Alpaste 891K”, 12.5 parts of butylcellosolve, 6.25 parts of hexyl cellosolve and 6.25 parts of “Shellsol71L”, and the mixture was stirred until the aluminum pigment washomogeneously dispersed. Then, 3.92 parts of the following resinsolution (III) (remark 4) and 0.2 part of methylethanolamine were addedto this mixture to neutralize it and stirred for one hour. Next, 40parts of the acryl emulsion (remark 2) was added to this mixture whilestirring, and 62.72 parts of deionized water was then added to dilutethe mixture, followed by stirring for one hour to obtain a mill base.

[0061] Added to 160 parts of the acryl emulsion (remark 2) were 33.33parts of “90% Cymel 327” and 57.14 parts of the 35% polyester aqueoussolution (remark 3), and the mixture was stirred for 15 minutes. Then,150 parts of the mill base described above was added thereto and stirredfor 30 minutes, and deionized water and methylethanolamine were thenadded to obtain a water based metallic coating material having a pH of8.4 to 8.5 and a solid matter content of 25%.

[0062] (Remark 4) Resin solution (III): A reactor equipped with astirrer, a temperature-controller and a condenser was charged with amixed solvent of 27.5 parts of methoxypropanol and 27.5 parts ofisobutanol, and it was heated to 110° C. and maintained at the sametemperature. Then, dropwise added to the mixed solvent described abovein 4 hours was 121.5 parts of a mixture comprising 25 parts of styrene,47.5 parts of n-butyl methacrylate, 7.5 parts of 4-hydroxybutylacrylate, 15 parts of the phosphate group-containing polymerizablemonomer (a1) (remark 1), 12.5 parts of 2-methacryloyloxyethyl acidphosphate (corresponding to the polymerizable monomer (b)), 10 parts ofisobutanol and 4 parts of t-butylperoxyoctanoate. Further, a mixturecomprising 0.5 part of t-butylperoxyoctanoate and 20 parts ofisopropanol was dropwise added thereto in one hour. Then, the mixturewas stirred and ripened for one hour to obtain a phosphategroup-containing resin solution (III). This resin had an acid value of83 mgKOH/g originating in a phosphoric acid group, a hydroxyl groupvalue of 29.2 mgKOH/g originating in 4-hydroxybutyl acrylate, a weightaverage molecular weight of 10,000 and a solid matter content of 50%.

[0063] Coating material performance test

[0064] Measurement of gas generating amount: put in the bottom of anErlenmeyer flask having a capacity of 300 ml was 150 g of the waterbased metallic coating materials obtained in Examples 3 and 4 andComparative Examples 1, 2, 3 and 4 (all of them had a solid mattercontent of 25% and a content of a flaky aluminum metallic pigment of8%), and a measuring pipette was inserted into the central part of thisvessel in an almost vertical direction. The lower end part thereof wasimmersed in the water based metallic coating material, and a space ofabout 5 mm was provided between the lower end part thereof and the flaskbottom. The outside of the measuring pipette and the inside of the cappart of the Erlenmeyer flask were tightly sealed with a cork stopper toshut it off from the outside with the inside of the measuring pipettecommunicating with the outside. It was stored at 40° C. for 10 days tomeasure a height of the water based metallic coating material in theinside of the pipette which was pushed up by pressure of gas generatedduring storage. The results thereof are shown in Table 1.

[0065] Coating film performance test

[0066] The water based metallic coating materials obtained in Examples 3and 4 and Comparative Examples 1, 2, 3 and 4 were coated on a steelplate on which a cationically electrodepositable coating material and anintermediate coating material were coated and cured by heating so thatthe film thickness was 15 μm, and the steel plate was left standing at aroom temperature for 2 minutes. Then, “Magicron KINO1001” (trade name,carboxyl group-containing acryl resin epoxy group-containingcompound-containing organic solvent base acid epoxy type clear coatingmaterial, manufactured by Kansai Paint Co., Ltd.) was coated thereon sothat the film thickness was 30 μm, and it was heated at 140° C. for 30minutes to cure both coating films at the same time. The double coatingfilm thus obtained was tested for a layer-to-layer adhesive property, awater resistance, a chipping resistance, a metallic appearance and aflip-flop property. The results thereof are shown in Table 1.

[0067] The tests were carried out by the following methods.

[0068] Layer-to-layer adhesive proverty:

[0069] The double coating film on the coated steel plate was cut by acutter so that it reached the base to make 100 cross-cuts having a sizeof 1 mm×1 mm, and an adhesive cellophane tape was adhered on the surfacethereof to investigate the number of the cross-cut coating filmremaining thereon after quickly peeling the tape at 20° C.

[0070] ◯: 100 cross-cuts remain

[0071] Δ: 99 to 90 cross-cuts remain

[0072] X: 89 or less cross-cuts remain

[0073] Water resistance:

[0074] The coated steel plate was dipped in warm water of 40° C. for 240hours and pulled up, and it was dried at a room temperature for 12hours. Then, it was tested in the same manner as that in thelayer-to-layer adhesive property test described above. It was evaluatedaccording to the same criteria.

[0075] Chipping resistance:

[0076] About 500 ml of crushed stones having a diameter of about 15 to20 mm was blown onto the double coated face at 20° C. at an air pressureof 4 kg/cm², and then the coated face was observed.

[0077] ◯: a little impact peeling is observed on a part of the clearcoating film

[0078] Δ: a little large impact peeling is observed on the clear coatingfilm and the metallic coating film

[0079] X: very large impact peeling is observed on the clear coatingfilm and the metallic coating film, and a large part of the intermediatecoated film is peeled off

[0080] Metallic appearance:

[0081] It is visually observed.

[0082] ◯: metallic pigment is aligned parallel to coated face andevenly, and metallic unevenness is not observed at all

[0083] Δ: a little metallic unevenness is observed

[0084] X: large metallic unevenness is observed

[0085] Flip-flop property:

[0086] Measured by means of a bending spectrophotometer “MA68”manufactured by X-RITE Co., Ltd. A Y value a at 15° and a Y value b at45° are determined, and they are applied to the following equation tocalculate the flip-flop property (FF):

FF=(a−b)/[(a+b)/2]

[0087] TABLE 1 Example Comparative Example 3 4 1 2 3 4 Gas generatingamount 0.1 0 20< 18.8 6.2 7 Layer-to-layer adhesive ◯ ◯ X X ◯ ◯ propertyWater resistance ◯ ◯ X X ◯ ◯ Chipping resistance ◯ ◯ X Δ Δ Δ Metallicappearance ◯ ◯ X X Δ Δ Flip-flop property 1.72 1.8 1.3 1.35 1.5 1.53

1. A phosphate group-containing resin obtained by copolymerizing: (a) apolymerizable monomer having a phosphate group represented by a formula[—OPO(OR)(OH)] (wherein R represents a hydrocarbon group having 4 to 10carbon atoms), (b) a polymerizable monomer having a phosphoric acidgroup represented by a formula [—OPO(OH)₂] and (c) a (meth)acrylate basepolymerizable monomer having two tertiary alkyl groups in a molecule,which is represented by:

wherein X represents hydrogen or methyl.
 2. The phosphategroup-containing resin as described in claim 1, wherein thepolymerizable monomer (a) is a compound having each at least onephosphate group represented by a formula [—OPO(OR)(OH)] andpolymerizable double bond in a molecule.
 3. The phosphategroup-containing resin as described in claim 1, wherein thepolymerizable monomer (a) is obtained by reacting one acidic hydroxylgroup contained in a phosphoric acid monoester represented by(HO)₂PO(OR) with a glycidyl group-containing compound having apolymerizable double bond.
 4. The phosphate group-containing resin asdescribed in claim 1, wherein the polymerizable monomer (b) is acompound having each at least one phosphoric acid group represented by aformula [—OPO(OH)₂] and polymerizable double bond in a molecule.
 5. Thephosphate group-containing resin as described in claim 1, wherein thepolymerizable monomer (b) is selected from the group consisting of(2-acryloyloxyethyl) acid phosphate, (2-methacryloyloxyethyl) acidphosphate, (2-acryloyloxyproyl) acid phosphate and(2-methacryloyloxyproyl) acid phosphate.
 6. The phosphategroup-containing resin as described in claim 1, obtained by furthercopolymerizing the other polymerizable monomer (d).
 7. The phosphategroup-containing resin as described in claim 6, wherein thepolymerizable monomer (d) is selected from the group consisting ofmethyl methacrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate,hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, glycidyl(meth)acrylate, (meth)acrylic acid, maleic acid, maleic anhydride,styrene, α-methylstyrene, vinyltoluene, (meth)acrylonitrile and vinylacetate.
 8. The phosphate group-containing resin as described in claim1, obtained by copolymerizing 0.5 to 30% by weight of the polymerizablemonomer (a), 1 to 35% by weight of the polymerizable monomer (b), 3 to35% by weight of the polymerizable monomer (c) and 0 to 95.5% by weightof the polymerizable monomer (d) based on the total amount of thepolymerizable monomers (a) to (d).
 9. The phosphate group-containingresin as described in claim 1, obtained by copolymerizing 1 to 20% byweight of the polymerizable monomer (a), 3 to 20% by weight of thepolymerizable monomer (b), 5 to 30% by weight of the polymerizablemonomer (c) and 30 to 91% by weight of the polymerizable monomer (d)based on the total amount of the polymerizable monomers (a) to (d). 10.The phosphate group-containing resin as described in claim 1, having aweight average molecular weight falling in a range of 3,000 to 100,000and an acidic value falling in a range of 20 to 140 mgKOH/g originatingin a phosphoric acid group.
 11. The phosphate group-containing resin asdescribed in claim 1, having a weight average molecular weight fallingin a range of 5,000 to 50,000 and an acidic value falling in a range of40 to 120 mgKOH/g originating in a phosphoric acid group.
 12. Thephosphate group-containing resin as described in claim 1, having anacidic value falling in a range of 100 mgKOH/g or less originating in acarboxyl group and a hydroxyl group value falling in a range of 0 to 120mgKOH/g or less.
 13. A water based metallic coating material compositioncomprising the phosphate group-containing resin as described in claim 1and a metallic pigment.
 14. The water based metallic coating materialcomposition as described in claim 13, comprising the phosphategroup-containing resin in an amount falling in a range of 0.1 to 15parts by weight in terms of a solid matter per 100 parts by weight ofthe metallic pigment.
 15. An article coated with the water basedmetallic coating material composition as described in claim 13.